The use of electrolytic capacitors in DC power electronics has been pervasive since early radio and television days. They provide the necessary function of smoothing voltage while conducting widely varying current. Electrically this may be achieved by having a large capacitance value. Chemically this large capacitance is accomplished by having an ionic conducting liquid as one of its plates. By nature these capacitors may dry out or have other issues causing short lifetimes compared to other commonly used power conversion components. The common approach to achieve the desired lifetimes for power conversion equipment is to provide huge operational margins so as not to overly stress the electrolytic capacitor. This only provides marginal improvement. This invention discloses an electrical circuit that may be useful in a wide variety of applications and which achieves the desirable benefit of smoothing while experiencing AC current ripple without the use of any short lifetime components. This circuit may use switchmode power conversion technology to also maintain low losses.
It can be helpful to understand the need for this invention in the context of a particular application, such as a solar power system or power factor correction circuitry as is often used internally in many varying devices. In merely an exemplary context of photovoltaic (PV) systems, many common PV converters may have typical lifetime limits of about five years or so. Such a lifetime may be inconsistent with the fact that PV panels or solar panels can in some instances need to be viewed from the perspective of generating their electricity savings for payback of initial investment over longer periods. The present invention provides systems that may in some embodiments address the lifetime limits for many current PV converters. It may provide systems that extend the lifetime of a grid tied PV converter for single phase power installation to lifetimes of even several decades.
At the current time the use of PV panels to generate electricity may be in a period of rapid growth. The cost of solar power may even be decreasing and many factors appear to limit the growth of non-renewable energy sources. Today there are both large scale systems and small scale systems being deployed. For the large systems power is often supplied in three-phase connections which may not require large amounts of energy storage per cycle. For smaller installations like residential, single phase power is frequently delivered. In a typical system, one or many PV panels may be connected to a grid-tied converter which may take the steady power from the PV panel, perhaps at its maximum power point, and may then transform it to AC power suitable to back-feeding the grid or other electrical power network. For single phase, power delivery energy storage may be required every cycle. Today this energy storage often accomplished with short lived components—electrolytic capacitors. The present invention overcomes this limitation in a manner that can practically increase the life of the PV converter componentry.